Porous, solid materials such as concrete, wood, gypsum, brick and like materials can become contaminated with semivolatile organic chemicals which pose a sizeable risk to human health. Semivolatile organic chemicals, such as fuel oil, diesel, and other transportation fuels, come in contact and can be absorbed into porous, solid materials, typically as a result of spills, leakage, and/or catastrophic floods. Other sources of contaminating semivolatile organic chemicals include household chemicals, solvents, pesticides, herbicides, insecticides, and other industrial chemicals that can be absorbed into porous materials due to commercial, industrial or home use. Semivolatile organic chemicals can also be absorbed into porous materials due to intentional acts of sabotage where these organic chemicals are used as chemical warfare agents or delivered in conjunction with other chemical warfare agents.
Past work has shown that non-aqueous phase liquids, both hydrophobic and hydrophilic, can get entrapped with water inside the pore spaces of materials and result in the formation of so-called “ganglia”. The concrete, brick, tile, and wood used in buildings are all porous materials that can become contaminated by these non-aqueous or organic chemicals. The problem of non-aqueous phase liquid removal from ganglia in contaminated porous materials has been addressed in a number of publications known in the art. Both light and dense hydrocarbons, as well as chlorinated solvents, have been efficiently removed by heating, steam extraction, permanganate or Fenton reagent oxidation, surfactant flushing, and/or various pump-and-treat technologies. These publications, however, are limited to particular kinds of soil, mostly clay and sand.
These technologies are not suitable to clean bulky, contaminated building materials that are porous, solid materials with pore sizes less than 1 micrometer. Furthermore, heating and steam treatments, instead of removing contaminants, will only force the contaminants deeper into the material. Alternatively, other methods such as chemical treatment by bleach and other oxidizing agents will not remove the chemicals trapped in pores at all, they will only be able to remove minor contaminants located on the surface.
The inefficiency of pump-and-treat technologies became evident during the cleanup activities associated with the devastating 1997 flood of Grand Forks, North Dakota. The basements and first story walls of many buildings were contaminated with fuel oil. After numerous treating and washing cycles, there was minimal or no apparent reduction of fuel oil vapors within the air space of the basements of the flooded buildings. As a consequence, owners were forced to demolish structurally sound buildings due to the unhealthy air space within the buildings. Therefore, it is desirable to develop a method to efficiently and effectively reduce the concentration of semivolatile organic chemicals from porous, solid materials.
Photocatalyst-induced removal of hydrocarbons has been used in applications where the contaminated substance is either liquid or air. In addition, the use of photocatalysts to destroy formaldehyde leakage from a wood layer was previously described in U.S. Pat. No. 5,604,339. The 5,604,339 patent was aimed at destroying formaldehyde, a harmful toxic high volatile organic compound. The high volatility of formaldehyde facilitated its relatively easy breakdown from surfaces of the wood.
The present invention, however, demonstrates how photocatalysts can be used to reduce the amount of semivolatile organic chemicals absorbed into porous, solid materials upon application of the photocatalysts to the surface, followed by excitation with a light source under aerobic conditions for a period of one day or longer.